This invention relates to chemical detection and, in particular, to chemical detection done by optical techniques.
Chemical detection is a necessity for many applications, particularly, as new chemical processes are developed and environmental concerns increase. Simple, rugged, inexpensive sensors are needed for industrial process control and environmental monitoring.
European Patent EP 0 061 884 A1 discloses a device for detecting changes in chemical or physical parameters using an optical fiber sensor and is incorporated herein in its entirety by reference. In the described device, the core of the fiber is surrounded by a cladding whose absorption spectrum varies with the composition of the surrounding material to be sensed. Light or photons enter one end of the fiber. The light exiting the other end of the fiber varies according to the chemical characteristics of the material in contact with the cladding. This results from coupling into the evanescent field of fiber.
Such a device provides both a rugged and compact sensor. However, in many real-world applications it can be difficult and/or time consuming to calibrate the sensor for a particular test environment. For example, tight bends in the sensor fiber can substantially alter the transmission characteristics of the fiber. Similarly, the temperature of the fiber affects the transmission. In some cases, it may even be difficult to determine if the fiber has been broken. In addition, noise and drift in the light source may cause erroneous readings.